On to Warmer Weather

March 31, 2008

SnapshotI noticed Seattle NWS put out a special statement this evening.  Seattle and Olympia had their coldest last week of March in history.  That would be daytime highs, not average daily temps.  I don’t have an intern, so I sat down on the computer and loaded up PDX’s highs since 1941.  Looks like it’s Portland’s coldest last week of March as well.  The next closest was 49.7 degrees in March 1967, the 3rd coldest was 1999 (50.0).  Winter 1998-1999 was a La Nina winter…what do you know!

Moving on, as I mentioned during the 10pm newscast I was very happy to come in today and see warm/dry weather on tap for the rest of the week.  This snowy period will be a distant memory in just a few days.  The upper-level ridging is not forecast to be that strong the rest of the week.  But in April all you need is no storms and no strong onshore flow to get nice & warm weather.

Long range models are all over the place beginning this weekend, so confidence is pretty low at that point.
..Mark Nelsen

Latest Snow in Portland?

March 28, 2008

Snapshot2There was some talk in the newsroom today about this maybe being the "latest snow in Portland".  So I spent lunchtime (Nalley’s Chili…only the finest), looking over snowfall data.  You can find PDX Snowfall Data on the Western Climate Data site.  Go to the bottom and you’ll find DAILY SUMMARY STATS, showing record snowfall for each day of the year.  All other Coop sites are on that web page as well if you back up a few menus.
All this is a bit academic, because no measurable snow was recorded at the weather service office today out on 122nd avenue anyway.  There was a trace today, but that is not written down in record books, as you can see in the link up above, so I don’t see how you can claim it’s the latest snow on record.  Since we’re friends, Rod Hill and I talk over the phone at times.  We had a little chat on the phone earlier about what a "trace" of snow means.  We had a mild disagreement (which means I think I’m right and he thinks he is).  We’ll have to have an old-fashioned Southern Duel eh?

So tonight we have a very cold airmass still streaming off the Pacific.  The 1st upper level low is moving into Eastern Washington, swinging an enhanced band of showers into N.W. Oregon and S.W. Washington this evening.  This could be the 1-2" producer for many of you in Clark County (that Steve Pierce is good!).  Other than that, it just looks like scattered snow showers tonight and again Sunday night.  In between it’s too warm at the lowest elevations to snow.

We’ll finally be done with all this snow talk by Monday morning.  Then it’s on to more normal Spring weather next week.  My "cool" forecast for next week (below 60 degrees) is based more on the ECMWF.  I fully admit that the GFS would give us temps well into the 60’s which would be quite nice after our current weather pattern.

Snow Totals: Spring Edition II

March 27, 2008

Okay, really, this is the last time for the season…snow totals for Friday, March 28th only please.

Into the comments go: New Snow, Location, Elevation

As of 1pm:

6.5"    Lee’s Camp    600′

3"        Corbett            1050′

2"        Washougal    1000′

4"        Washougal      850′

2"        Sandy             1000′

2"        Tillamook        S. Level

2"        Rose Lodge     200′

2"        Council Crest   900′

1"        Sylvan                750′

1"        Happy Valley    500′

1/2"    Orchards            200′

1/2"    S.W. Portland    700′


Snow on March 28th?

March 27, 2008

SnapshotI feel like it’s time for one of those "sample" tests.  The ones that don’t really count, but you take them to see how your skills are coming along.  Why the heck am I wound up about snow or a surprise snowstorm in Portland, Oregon on March 28th???  That thought actually makes the forecasting easier, thinking that 7 days from now we could hit 75 or 80 degrees (first week of April).  But, back to reality.

Very complex and messy forecast with a high potential for being wrong some areas and right on others in the morning.  So the 00z runs are out and STILL in some reasonable disagreement tonight.  Both GFS and NAM take a low across Southern Oregon tomorrow, of course the NAM continues to be significantly deeper.  But there is a 2nd, weaker low that approaches the Washington Coast at the same time late tonight and tomorrow.  In reality it’s almost more like a negative tilt front with a wind swith line from easterly to gusty westerly.  It passes through the metro area about midday tomorrow.  From now until midday, we have light or calm wind.  No significant east or southerly wind (plus there is no cold air to our east in late March, so the easterly wouldn’t help anyway).  A cold atmosphere modifies only slightly the next 12 hours, so all we need is steady, heavy precipitation to drag a very wet snow level down to sea level in the first few hours of daylight.  The MM5-GFS is more impressive with precipitation, bringing snow down to the Valley floor, the NAM a bit slower, which would say no snow anywhere below 1,000′.  I’m leaning more towards the GFS with it’s track record.  You see my forecast above, it applies to all areas West of the Cascades, including the Coastline, in Northwest Oregon and S.W. Washington.

As I’ve mentioned in the last few months, I’m done with that 200′, 500′, 700′ snow level crap that was so useless this winter for many.  I just think we’ll have heavy, wet snowflakes from 5-9am, with some sticking possible, but temps bottoming out near 35 in the city and 32 at the top of the West Hills.  The North Coast is in a very interesting spot with light morning wind and even heavier precip. right under the front.  Could it be a widespread 2-4" even to the beaches out there?  Tough call.  If the northern low is slightly too strong, then a weak onshore breeze will be present all night and through the heavy precip.  No snow in that case.  But I’ll stick with the Trace-1" forecast out there in the end.

Saturday and Sunday look far more showery, so it should be like this morning, with random spots each morning getting a dusting.  Amazing how strong the sun is.  An airmass cold enough to bring a dusting to the lowest elevations at night, but a high of 50 by late afternoon, then back to snow the next night.  What a battle between solar insolation and the very cold upper-level airmass.  If today was a winter day, we would have had a 38-40 degree high at PDX, even with the sun.

A bit more reasonable next week with temps recovering to near normal…which is about 58 for the first few days of April in Portland…Mark Nelsen

Snow Totals: Spring Edition

March 27, 2008

Okay…back in the saddle this afternoon.  I thought early February was the last time we would do this, but one LAST time for this season here we go:

1.  New Snow Depth

2.  Location

3.  Elevation (if you know it)


Comp Day Extra

March 25, 2008

Slp_63_0000 Slp_72_0000_3 I’m currently using up 3 "comp" days…basically taking 3 days off in exchange for working that snowy Sunday back in late January plus this past weekend.  My daughter had a planned preemptive surgery at Emanuel hospital today, so yesterday and today I didn’t look very closely at maps.  But after running into several people at the hospital that thought it was going to snow in Portland soon, I figured I better take a look.  The last I had checked it appeared that we’d see -7 850mb temps and snow sticking maybe down to around 1,500′ sometime Wednesday-Friday.

So what do I see?  Lots of interesting weather possibilities, which may or may not have an impact on normal folks here in Portland. 

First, the snow:  The forecast 850mb temps haven’t changed from what was shown Sunday for late this week.  At the end of March, to get STICKING snow down to the lowest elevations, you’d need all parameters to come together perfectly.  Steady, heavy precipitation sometime between the hours of 10pm and 8am (nighttime), no mixing south wind, and that cold atmosphere we know is coming.  First off, let’s remember the NAM has not done well this winter and in general doesn’t do as well as the GFS (for sure on low pressure placement!).  It shows a comma-type trough feature moving into the southern/central Valley late tomorrow afternoon, turning winds light through the Valley too.  This is very similar to the sudden 1-3" that fell one night this past winter from Woodburn to Eugene.  The 00z GFS has the trough a bit farther north, keeping the mixing wind going, plus the timing isn’t during the night, so we’ll get 40-45 degree rain in the city tomorrow afternoon.  I doubt we’ll get anything more than a dusting from 1,000-1,500′ between the Coast Range and Cascades the next 24 hours.  Maybe nothing at all below 1,500′.  I bet the west slopes of the Coast Range will see sticking snow down to 1,000′ since the precipitation will be more intense out there.  Thursday should be much more showery with sunbreaks.  This time of year we’ll be in the 45-50 degree range, so the snow level jumps up to at least 2,000-2,500′ in the afternoon, very similar to last Saturday.  Friday is very interesting with a surface low forecast to track towards the N. Oregon Coast, then move inland into S.W. Washington.  If the low is approaching the Coast in the early morning hours (before 8am), the brief offshore flow and steady, heavy precipitation COULD bring snow below 1,500′.  That’s a big IF.  So in general…those of you in the hills around 1,500′ will probably get a few shots of snow the next few days, with a dusting possible to 1,000′ in the late night hours.  Better chance for a dusting below 1,000′ in the Coast Range and Cascade Foothills.  Forget about it in the city…it would have to be a one-time freak occurrence.  It would be as crazy as…having a tornado in January in Vancouver…

A new wrinkle this evening is about possible strong wind:  As I mentioned, the 00z GFS MM-5 brings a surface low (while deepening) up into S.W. Washington Friday morning.  The 10-12 mb OLM-EUG gradient could produce south wind gusts of 30-40 mph.  The 00z NAM goes nutso…deeping the low to 985 mb up around Centralia.  This gives 20-24 mb. in the same area!  That’s major windstorm territory for the KLS-EUG corridor.  BUT…it’s the NAM, so I would discount it for now, but there’s always 12z right?  I’ve included both maps for comparison.  Okay, checking out for now, maybe an update tomorrow evening again…Mark Nelsen

A Wet Week Ahead

March 21, 2008

SnapshotI don’t know how many of you look at these maps, but sometimes they are quite useful.  This is the GFS 12z Ensemble Spaghetti Chart for hour 168…next Friday.  It shows the 558 dm 500mb height line for each of the ensemble members.  Basically the model is run many times (something like 20?) after the initial conditions are changed slightly or "perturbed".  We often get an idea of how confident models are of future weather patterns by seeing how well the different "versions" line up.  What I notice today is a heck of an agreement for westerly flow continuing through all of next week.  That’s unusual for 7 days out in time.  Usually the different ensemble members are really diverging after 4-5 days.  Notice how the lines are clustered very tightly in the Eastern Pacific and into California/Oregon.  So what does it mean?  It’s going to be wet and cool for Oregon’s Spring break.  You can find the spaghetti charts on my model page here.  As always, you can click on the picture here for a larger view too.

I’m posting early today because I’m procrastinating doing the weather graphics for a few minutes…a rare moment of inspiration.

Enjoy the bright and warm sunshine tomorrow.  It still looks like 60 degrees or so in the afternoon.  Cold front moving in Sunday brings the opening round of the next rainy period.  I’m working this weekend for Stephanie too, so if I get REALLY inspired, I might post again…Mark Nelsen